1. Field of the Invention
The present invention relates to a coupling apparatus (receptacle) of a light emitting element such as a laser diode and an optical fiber. The present invention also relates to a method for adjusting optical fiber position using the same.
2. Description of the Related Art
Recently, laser drawing apparatuses using multi-laser beams have been proposed in which a group of light sources consisting of a plurality of laser emitters and a plurality of optical fibers are provided to increase the drawing speed.
In a multi-laser beam drawing apparatus using optical fibers as a light source, the laser beam emitted from the semiconductor laser and made incident upon the incident surface of the optical fiber is partly reflected by the incident surface. If the reflected light is made incident upon the semiconductor laser, the laser emission is disturbed, thus resulting in a change in the intensity of the laser beams, etc. To avoid this, the incident surface of the optical fiber is cut along a plane inclined with respect to the center axis of the optical fiber to form an oblique incident surface, so that the light reflected thereby does not reach the semiconductor laser, as shown in FIG. 4.
In the prior art shown in FIG. 4, a laser diode (LD) 156 is secured to a lens holder 116 which holds a coupling lens 136 through an LD holder 126. The lens holder 116 is provided with an adjusting ring 166 secured thereto. The optical fiber 20 is held by a ferrule 196 so that the center axis of the optical fiber at the incident surface thereof is inclined with respect to the optical axis of the coupling lens 136 at a predetermined inclination angle. The ferrule 196 is press-fitted in the adjusting ring 166 which is secured to the lens holder 116. The incident surface of the optical fiber 20 is defined by an oblique surface 20a inclined at a predetermined inclination angle with respect to a plane perpendicular to the center axis thereof. The optical fiber 20 is held in such a way that the incident surface 20a thereof is not normal to the optical axis O1.
The ferrule 196 which holds the optical fiber 20 is not parallel with the optical axis O1 of the coupling lens 136 and is moved in the direction parallel with the center axis of the optical fiber 20 to adjust the position of the incident surface (core surface) 20a of the optical fiber 20. However, since the direction of the movement of the optical fiber 20 is inclined with respect to the optical axis O1, if the ferrule 196 is slid to move the incident surface 20a to the focal point of the coupling lens 136, not only does the distance between the incident surface 20a and the coupling lens 136 in the optical axis direction change, but also the distance between the center of the incident surface 20a and the optical axis O1 also varies. Consequently, it is difficult to adjust the incident surface 20a of the optical fiber 20 to the focal point f of the coupling lens 136.
Moreover, to establish a highly precise positional relationship between the laser diode 156 and the optical fiber 20 at the connection therebetween, the LD holder 126 and the adjusting ring 166 are independently moved along the contact surfaces thereof with the lens holder 116 in the prior art. Upon completion of the adjustment, the LD holder 126 and the adjusting ring 166 are welded to the coupling lens holder 116, for example, by a YAG laser to prevent the accidental movement thereof. Therefore, if the laser diode 156 is broken, it is difficult to replace the laser diode alone. Upon replacement of the broken LD 156, if the LD holder 126 is detached from the lens holder 116 without detaching the adjusting ring 166 to which the ferrule 196 and the optical fiber 20 are secured from the lens holder 116, it is difficult to readjust the position of the incident surface 20a of the optical fiber 20, as mentioned above.
The emission surfaces of the light sources are united in the form of a fiber array. Therefore, if a laser diode of one of the light sources is broken, it is difficult to repair or replace the LD since the laser receptacle cannot be disassembled. Furthermore, since the fiber array cannot be disassembled, the entirety of the laser sources must be replaced in spite of the fact that the remaining fibers are normal.
It is possible to secure the adjusting ring 166 to the lens holder 116 by means of screws in place of welding. However, the relative position therebetween may be changed due to the force produced in the rotation direction or forward movement direction of the screws when the screws are fastened or loosened.